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| -rw-r--r-- | llvm/docs/LangRef.rst | 25 |
1 files changed, 15 insertions, 10 deletions
diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst index c81abb3..99f3ec2 100644 --- a/llvm/docs/LangRef.rst +++ b/llvm/docs/LangRef.rst @@ -1360,11 +1360,13 @@ Currently, only the following parameter attributes are defined: accessed, during the execution of the function, via pointer values not *based* on the argument or return value. This guarantee only holds for memory locations that are *modified*, by any means, during the execution of - the function. The attribute on a return value also has additional semantics - described below. The caller shares the responsibility with the callee for - ensuring that these requirements are met. For further details, please see - the discussion of the NoAlias response in :ref:`alias analysis <Must, May, - or No>`. + the function. If there are other accesses not based on the argument or + return value, the behavior is undefined. The attribute on a return value + also has additional semantics described below. The caller shares the + responsibility with the callee for described below. The caller shares the + responsibility with the callee for ensuring that these requirements are met. + For further details, please see the discussion of the NoAlias response in + :ref:`alias analysis <Must, May, or No>`. Note that this definition of ``noalias`` is intentionally similar to the definition of ``restrict`` in C99 for function arguments. @@ -6816,7 +6818,9 @@ tuples this way: A memory access with an access tag ``(BaseTy1, AccessTy1, Offset1)`` aliases a memory access with an access tag ``(BaseTy2, AccessTy2, Offset2)`` if either ``(BaseTy1, Offset1)`` is reachable from ``(Base2, -Offset2)`` via the ``Parent`` relation or vice versa. +Offset2)`` via the ``Parent`` relation or vice versa. If memory accesses +alias even though they are noalias according to ``!tbaa`` metadata, the +behavior is undefined. As a concrete example, the type descriptor graph for the following program @@ -6936,9 +6940,9 @@ does not carry useful data and need not be preserved. noalias memory-access sets. This means that some collection of memory access instructions (loads, stores, memory-accessing calls, etc.) that carry ``noalias`` metadata can specifically be specified not to alias with some other -collection of memory access instructions that carry ``alias.scope`` metadata. -Each type of metadata specifies a list of scopes where each scope has an id and -a domain. +collection of memory access instructions that carry ``alias.scope`` metadata. If +accesses from different collections alias, the behavior is undefined. Each type +of metadata specifies a list of scopes where each scope has an id and a domain. When evaluating an aliasing query, if for some domain, the set of scopes with that domain in one instruction's ``alias.scope`` list is a @@ -7695,7 +7699,8 @@ If all memory-accessing instructions in a loop have ``llvm.access.group`` metadata that each refer to one of the access groups of a loop's ``llvm.loop.parallel_accesses`` metadata, then the loop has no loop carried memory dependencies and is considered to be a -parallel loop. +parallel loop. If there is a loop-carried dependency, the behavior is +undefined. Note that if not all memory access instructions belong to an access group referred to by ``llvm.loop.parallel_accesses``, then the loop must |